PROIDED. Substance use disorders (SUD) co-occurring with borderline personality disorder (BPD) pose serious and complex public health problems. Dialectical BehaviorTherapy for SubstanceAbusers (DBT-S)is a comprehensive psychosocial treatment, efficacious for substance-dependent individuals with borderline personality disorder (BPD). In Phase I, we developed and evaluated an innovative computer-based training (CBT) prototype of DBT-S Behavioral Chain Analysis (BCA) for drug treatment providers using an iterative process of prototype development. We tested the prototype's efficacy in a pilot randomized controlled trial (RCT) comparing DBT-S CBT (n=12) to control CBT (n=13) in a sample of treatment providers from routine drug treatment program. Results demonstrated the DBT-S CBT was efficacious at producing knowledge gains, recall of course strategies,increased self-efficacy among treatingdrug-addicted BPD patients, and promoting skill use in the subsequent weeks. We propose to significantly expand the course content and its evaluation in Phase II. We will again use an iterative process of development, relying on extensive end-user testing as well as feedbackfrom a panel of scientific and DBT experts. Upon completion, we will begin a RCT evaluation (N=120) where we will compare the CBT (n=40) to other standard training methods, specifically instructor-led training (n=40) and text (n=40). In addition to the outcome variables assessed in Phase I, we will include a performance- based test of clinical application where role-plays will be video taped and coded for adherence.